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CHARACTER DISPLACEMENT IN THE RADIOLARIAN GENUS, EUCYRTIDIUM
... As the univariate models in evoTS are natural extensions and modifications of the models in paleoTS, I start by introducing the univariate models available in paleoTS before I explain the expanded univariate models implemented in evoTS. I then apply these models to a well-known and previously published dataset, the evolution of size in the radiolarian lineage Eucyrtidium calvertense during allopatry and in a subsequent phase of neosympatry with its sister lineage Eucyrtidium matuyamai (Kellogg 1975). I continue by introducing the multivariate models implemented in evoTS before I apply them in a reanalysis of a published dataset of two armor traits in a stickleback lineage (Bell et al. 2006;Hunt et al. 2008). ...
... Background Kellogg (1975) investigated whether size evolution in the radiolarian lineage Eucyrtidium calvertense showed trait dynamics consistent with a scenario of character displacement (Fig. 2). Eucyrtidium matuyamai evolved from E. calvertense in subarctic waters, and the two lineages differentiated during a period of allopatry. ...
... During this neosympatric phase, the two lineages differentiated in size, with E. matuyamai evolving to become about 25% larger and E. calvertense to become about 10% smaller. Kellogg (1975) concluded that the evolutionary sequence of E. calvertense in subtropical waters showed little net change during the allopatric phase, but a trend toward smaller size in the neosympatric phase, a type of trait dynamics Kellogg (1975) interpreted to be consistent with the process of character displacement. The evolutionary sequence spans 3.67 Myr and consists of 49 samples with median and mean numbers of measured specimens per sample of 25 and 25.4, ...
The nature of phenotypic evolution within lineages is central to many unresolved questions in paleontology and evolutionary biology. Analyses of evolutionary time series of ancestor–descendant populations in the fossil record are likely to make important contributions to many of these debates. However, the limited number of models that have been applied to these types of data may restrict our ability to interpret phenotypic evolution in the fossil record. Using uni- and multivariate models of trait evolution that make different assumptions regarding the dynamics of the adaptive landscape, I evaluate contrasting hypotheses to explain evolution of size in the radiolarian Eucyrtidium calvertense and armor in the stickleback Gasterosteus doryssus . Body-size evolution in E. calvertense is best explained by a model in which the lineage evolves as a consequence of a shift in the adaptive landscape that coincides with the initiation of neosympatry with its sister lineage. Multivariate evolution of armor traits in a stickleback lineage ( G. doryssus ) shows evidence of adaptation toward independent optima on the adaptive landscape at the same time as traits change in a correlated fashion. The fitted models are available in the R package evoTS, which builds on the paleoTS framework.
... Three possible examples have been illustrated among mammals, involving the Paleocene primate Plesiadapis (Gingerich 1976), the early Eocene condylarth Hyopsodus (Gingerich 1974(Gingerich , 1976, and the early Eocene primate Cantius (="Pelycodus"; Gingerich 1976Gingerich , 1980. Kellogg (1976Kellogg ( , 1983 describes another important example in the Plio-Pleistocene radiolarian Eucyrtidium (Fig. 4). In all four cases, a well-sampled stem lineage is known, composed of many individuals and increasing gradually in size through time or fluctuating gradually about some average value. ...
... Entire sequence shown here represents about 3.5 ma of evolutionary rime. Data and interpretation are from Kellogg ( 1976Kellogg ( , 1983, replotted ro make rares and trends comparable wirh those of Eocene mammals shown in Figs. I and 2. Examination of other cores indicates that Eucyrtidium matuyamai evolved from a population of E. calverlense isolated north of the subarctic convergence for a short rime 1.9 ma before present (Hays 1970;Kellogg 1976). ...
... Data and interpretation are from Kellogg ( 1976Kellogg ( , 1983, replotted ro make rares and trends comparable wirh those of Eocene mammals shown in Figs. I and 2. Examination of other cores indicates that Eucyrtidium matuyamai evolved from a population of E. calverlense isolated north of the subarctic convergence for a short rime 1.9 ma before present (Hays 1970;Kellogg 1976). Generic and possibly some morphological difference making E. matuyamai and E. cal11er1en1e distinct as semispecies (sensu Mayr 1963) were probably established rapidly in alloparry, bur acquisition of sufficient morphological difference to make these full species apparently occurred when the rwo secondarily became partially or entirely symparric. ...
Morpholocial continuity in the fossil record is the principal evidence favoring evolution as a historical explanation for the diversity of life. Continuity is usually discussed on scales broader than the species level. Patterns of morphological variation characteristic of living species are useful in recognizing species on time planes in the fossil record, but the fossil record is rarely complete enough temporally or geographically to preserve more than a fraction of species living in a given interval. Transitions between known species are even rarer. Where transitions are preserved, new species appear to arise through anagenesis and cladogenesis. Evolutionary species are often necessarily bounded arbitrarily in the dimension of time. Orthogenesis and punctuated equilibrium lie at opposite poles in a spectrum of speciation modes. Orthogenesis, highly constrained anagenesis, is probably rare. Cladogenesis appears to differ little from anagenesis once ancestral stocks are segregated. Limited evidence suggests that morphological differentiation during cladogenesis postdates genetic isolation. Hence, punctuated equilibrium may be rare as well. Rates of evolution vary and rate distributions are truncated and biased by limits of stratigraphic completeness and time resolution: moderate to high rates of morphological evolution and species turnover are rarely recorded by fossils. Species durations are poorly characterized, but they appear to be so variable that there is no suggestion of periodicity. Species longevity is unpredictable. The episodic nature of faunal turnover suggests that extrinsic environmental factors rather than intrinsic homeostatic factors govern evolution at the species level.-from Author
... The fossil record of phyletic evolutionary morphotypes is characterized by cases where the descendant almost completely replaces its direct ancestor within a short stratigraphic interval (Fig. 1B). Meanwhile, cladogenetic speciation is an evolutionary splitting event of a new descendant from its direct ancestor (Kellogg and Hays, 1975;Kellogg, 1976;Fig. 1C). ...
... (B) Phyletic evolution of the Didymocyrtis phylogenetic lineage (referred to Suzuki and Aita, 2012). (C) Cladogenetic speciation of Eucyrtidium matuyamai from Eucyrtidium calvertense (revised after Kellogg, 1976). ...
... Nonetheless, his analysis revealed no evidence for competitive character displacement in either body size or bill size. Since Grant's (1972) review, several papers have appeared which purport to demonstrate ecological character displacement Berry, 1975;Fenchel, 1975;Kellog, 1975;Husar, 1976). None of these studies partitions the variation into a component explained by sympatry and a component explained by other factors . ...
... The authors argue that the fossil record is superior to the Recent time slice for demonstrating patterns of variation among populations, but since they fail to sequence their samples chronologically, their time slice is merely thicker, not more informative. A more convincing example of morphological character displacement in the fossil record is offered by Kellog (1975). This example involves the radiolarian species Eucyrtidium matuyamai and E. calvertense from a pair of North Pacific deep sea cores of Miocene to Recent age. ...
https://deepblue.lib.umich.edu/bitstream/2027.42/137612/1/evo04742.pdf
... only overlaps biogeographically 'with the ancestral form in a narrow transition zone. The evolution of E. matuyami from E. calvertense has been interpreted by the authors as an example of allopatric speciation (Hays 1970;Kellogg 1976Kellogg , 1983). Yet the oceanographic barrier separating the two regions is far too weak to serve as an effective barrier for allopatry (Pierrot-Bults and van der Spoel 1979), while the existence of a zone of biogeographic overlap throughout the speciation event (Hays 1970, fig. ...
... The first example was studied by Hays (1970) and Kellogg (1976), who followed the divergence of the radiolarian Eucyrtidium matuyami from its ancestor E. calvertense. The ancestral species is fairly cosmopolitan but restricted to waters south of the North Pacific frontal system. ...
The punctuated equilibrium hypothesis is one of many possible paleontologic patterns of speciation which may be tested against the deep-sea fossil record of planktonic microfossils. The nature of reproduction and variation within a species has a profound effect on its expected tempo and mode of evolutionary change. Biologic data on pelagic plankton and on protistan genetics and reproduction suggest that speciation in pelagic holoplanktonic protists may also be parapatric, 'equal' allopatric, or the result of hybridization. Each of these models makes testable predictions of paleontologic pattern. Published records of speciation in planktonic deep-sea microfossil data are compatible with these alternative models. Existing data sets are not yet sufficiently complete to provide strong tests. -from Author
... Diatom assemblages record an increase in Actinocyclus oculatus, whose ecological affinities can be inferred to be close to those of its taxonomical junior synonym, A. robustus (Shimada et al. 2009), presently growing in the low-saline, cold, and well-stratified waters of the modern Okhotsk Sea (Sancetta, 1982;Sancetta and Silvestri, 1986;Shiga and Koizumi, 1999). The radiolarian stratigraphy is characterized by the LO of the subarctic Eucyrtidium matuyamai ( Table 2; Kamikuri et al., 2007;Morley and Nigrini, 1995;Shilov, 1995), which has been proposed to be a morphological adaptation to cold and nutrient-poor waters in the subarctic Pacific (Hays, 1971;Kellogg, 1975). Cold oceanic and climatic conditions after 1.7 Ma are consistent with ice sheet growth, as documented by the concomitant increase in IRD at ODP Sites 887 (Fig. 2) and 882 (Sigman et al., 2004;Haug et al., 2005). ...
Analyses of marine palynomorphs, including dinocysts and acritarchs, from Pliocene-Pleistocene sediments of the Ocean Drilling Program (ODP) Site 887 in the Gulf of Alaska allowed the development of a biostratigraphic scheme, which we compared with bio-events in regional diatom and radiolarian zonations. The dinocyst biostratigraphic scheme includes five biozones and four major boundaries. A first stratigraphic boundary, at 4.4 Ma, is associated with a change in productivity. The other boundaries, at 2.7 Ma, 1.7 Ma, and 0.7 Ma, correspond to the onset of the modern halocline, an intensified cooling period, and the end of the Mid-Pleistocene Transition respectively. Moreover, the analyses of dinocyst assemblages illustrate long-term changes in the surface ocean after 5.3 Ma. The occurrence of Ataxiodinium zevenboomii, Impagidinium velorum, and Impagidinium patulum suggests warm-temperate conditions until approximately 4.2 Ma. Between 4.2 and 2.7 Ma, colder and less saline events marked by an increase in cold-tolerant species, such as Habibacysta tectata, suggest regional cooling and/or lower salinity of surface water, which might be related to Alaskan glacier meltwater discharges. From 2.7 to 1.2 Ma, the presence of Impagidinium pallidum and cysts of Pentapharsodinium dalei suggests low-salinity, cold, and stratified surface waters, whereas major drops in dinocyst fluxes are linked to a decrease in productivity and harsh conditions. Progressive change from cold, stratified waters to warmer and saltier conditions occurred between 1.2 and 0.7 Ma during the Mid-Pleistocene Transition. After 0.7 Ma, dinocyst assemblages are characterized by the alternating dominance of Brigantedinium spp. and Operculodinium centrocarpum, suggesting fluctuations between nutrient-rich, low-salinity, cold waters and cool-temperate environments.
... -Microevolutionary studies that have tested the contending theories of punctuated equilibrium and phyletic gradualism have generally focused on benthic macrofossils (e.g., Cheetham, 1986;Stanley and Yang, 1987) or pelagic microfossils (e.g., Ozawa, 1975;Kellogg, 1976;Lazarus, 1986). Graptolites, as colonial planktonic macrofossils, represent a group whose microevolutionary processes have received very little attention. ...
The Orthograptus quadrimucronatus species group currently comprises 22 taxa, which, with the exception of O. ruedemanni , are distinguished from other orthograptids by the presence of paired apertural spines on their thecae. A detailed morphometric analysis of this group indicates that these taxa comprise four basic morphotypes that actually represent only six distinct species: O. pageanus, O. quadrimucronatus, O. spinigerus, O. ruedemanni, O. eucharis , and O. rivai.
Specimens of Orthograptus pageanus have a rapidly widening rhabdosome with elongated spines on the first two or four thecae. Orthograptus pageanus is divided into two chronological subspecies, an older, smaller form, O. pageanus pageanus , and a younger, larger form, O. pageanus maximus n. subsp. Specimens of O. spinigerus have elongated spines on one or two thecal pairs between the sixth and thirteenth thecal pairs, a very narrow proximal end, and a rapidly widening rhabdosome. Specimens of O. quadrimucronatus have a more parallel-sided shape and no unusually long spines. The subspecies O. quadrimucronatus richmondensis is differentiated by the absence of both a median septum and a th 1 ² spine. Orthograptus ruedemanni, O. rivai , and O. eucharis are all dwarf forms.
Within a chronostratigraphic framework based on K-bentonite bed correlations the pattern and process of evolutionary change in the members of the O. quadrimucronatus species group is examined. Morphometrically, each species remains a coherent entity through time, occupying its own distinct morphospace. Each speciation event probably occurred rapidly, precluding the preservation of intermediates, and the new species retained their basic morphology throughout their existence. Within these lineages, phyletic changes were either absent or encompassed only changes in size, even when accumulated for much longer intervals than would be expected for speciation events. These patterns appear to be consistent with the evolutionary model of punctuated equilibrium.
... Interpretations of evolutionary phenomena in the fossil record are highly dependent on the quality and completeness of the stratigraphic record. Hence, many of the more rigorous analyses of pattern and process have come from the relatively recent marine record (e.g., Kellogg, 1976;Cheetham 1987;MacLeod 1991;and Jackson and Cheetham 1994). The pattern of graptoloid turnover in the Mohawkian and Cincinnatian rocks of New York has been well documented (Riva 1969(Riva , 1974Goldman et al. 1994), but the processes responsible for producing this pattern have not been carefully examined. ...
The stratigraphic distribution of graptoloid species within the upper Middle Ordovician strata of New York State represents a complex pattern of origination, extinction, faunal migration, and fluctuating relative abundances. In particular, the observed patterns of species turnover at graptolite biozone boundaries are apparently strongly correlated with lithofacies, sampling strategies, and the depositional effects of relative sea-level change.
Vertical facies changes that occur within third-order depositional sequences and fourth- or fifth-order parasequences are mirrored by changes in the graptoloid faunal composition. Large-scale faunal turnovers at biozone boundaries tend to occur either at sequence boundaries or at flooding surfaces within sequences (e.g., the base of Highstand System Tracts). The base of the Corynoides americanus and Climacograptus (D.) spiniferus Zones coincide with major onlap events, and the Orthograptus ruedemanni Zone fauna appears just below a Lowstand Systems Tract. Within individual biozones, smaller-scale changes such as the fluctuating relative abundances of graptoloid species coincide with higher-order parasequence cyclicity. These distribution patterns resemble recent computer-generated models for the sequence stratigraphic distribution of hypothetical taxa.
By combining good biogeographic control with a detailed sampling program, we are able to see through the patterns attributable to depositional cyclicity and identify the different components of faunal turnover (migration, speciation, and extinction).
... Population genetic theory tells us that if mutation generates neutral variation in a character, the mean will vary (drift) over time; it cannot remain fixed in a finite population. Indeed, fossil lineages of radiolarians show phenotypic variance within populations and change in the mean over time (Kellogg 1975, Lazarus 1983. If a character is capable of varying (as it clearly is, if it varies among related species), stasis requires a stabilizing factor, and some form of selection must be the leading hypothesis. ...
... Evidence that divergence has occurred between competitors comes from the fossil record (Eldridge 1974, Kellogg 1975, Schindel and Gould 1977. While these examples are interesting, they provide no evidence that competition was necessarily the mechanism, nor that the divergence had a genetic basis. ...
That niches of competitors in ecological communities are shaped by mutual coevolution, which thus allows many species to coexist, is a commonly-held view. Two species must live together consistently to coevolve, so since predators (or parasites) are dependent upon their prey, they will necessarily co-occur with them and so should coevolve. In contrast, competing species, which are not dependent on each other, need not consistently co-occur or coevolve. Increased diversity, by reducing the consistency of co-occurrence, also reduces the chance of coevolution. To demonstrate coevolutionary divergence of competitors one must show: 1) that divergence has actually occurred: this has been done for some fossil sequences but not for any extant competitors; 2) that competition, rather than some other mechanism, is responsible; and 3) that it has a genetic basis. To demonstrate 2) and 3) for natural populations requires appropriate field experiments, which are suggested in the paper. This has been done, in part, in only one case. Thus the notion of coevolutionary shaping of competitors' niches has little support at present. Theory and evidence suggest that it is probable only in low diversity communities. /// То, что ниши конкурентов в экологических сообщаствах оформились в процессе коэволюции, поэволяющей т.о. сосуществовать многим видам, общепринятая точка зрения. Два вида должны сосуществовать, последовательно коэволюционируя, так что, по-скольку хищники (или паразиты) зависят от своих жертв, они должны непременно встречаться вместе и т.о. могут коэволюционировать. В противоположность этому, конкурирующие виды, независимые друг от друга, наобязательно должны встречаться вместе и коэволюционировать. Повышение разнообрязия при снижении постоянства совместной встречаемости таюже снижает возможность коэволюции. Для демонстрации коэволюционной дивергенции конкурентных видов следует показать: 1. что дивергенция реально существует; это было сделано для некоторых ископаемых рядов, но не для современных конкурирующих форм. 2. что конкуренция более реактивна, чем любой другой механизм; 3. и что она имеет генетическую основу. Чтобы доказать второй и третий пункты для естественных популяций, необходимо проведение полевых экспериментов, которые предложены в статье. Это было частично проделано лишь в одном случае. Таким образом, представление о формах коэволюции ниш конкурирующих видов плохо обосновано. Теория и имеющиеся факты говорят о том, что это возможно лишь для сообществ с низким разнообразием.
... Finally, 1 would like to suggest that the possibility of testing the 'hypothesis of peripheral evolution' by biostratigraphy may not be quite so hopeless as the authors believe. 1 found a clear case of allopatric speciation in the Radiolaria of North Pacific deep-sea sediments (Kellogg 1976). and I believe that additional cases will be discovered as more complete sedimentary sequences (as in hydraulic piston cores) become available and as a more concerted effort is made to look for ancestors outside of the sequence under immediate examination. ...
... Morphometric studies of radiolarians have been used in several fields including critical evaluation of the 'punctuated equilibria' hypothesis of evolution (Kellogg, 1976(Kellogg, , 1983, and other evolutionary and taxonomic issues (Lombari and Lazarus, 1988;Granlund, 1990), as well as regional-scale distributions of different morphotypes (Granlund, 1986;Swanberg and Bjorklund, 1987). In this study, a morphometric approach has been applied to Actinomma bore& (Cleve), one of the most common polycystine radiolarian species in the Northern Oceans. ...
A morphometric study on the polycystine radiolarian species Actinomma boreale (Cleve) from ten trigger weight core-tops from the Norwegian-Iceland Seas, three piston cores taken offshore western Norway and three surface sediment samples from Lygrepollen, Sogndalsfjord and Høyangsfjord (western Norwegian fjords) shows a variation in morphology that groups A. boreale into three distinct clusters, interpreted to be related to different oceanographic settings. The largest specimens of A. boreale are found in the western Norwegian fjords, the smallest in the Iceland Sea, giving an apparent positive correlation with temperature.Down core studies in piston cores from the Norwegian Sea demonstrate a considerable size variation of the cortical shell of A. boreale. In the eastern Norwegian Sea, the climatically cold Younger Dryas had a population of A. boreale that was characterized by large cortical shells, while the climatically warm Holocene population was dominated by small sized cortical shells, showing a negative correlation with temperature. We suggest that the large sized conical shell population of A. boreale in the Younger Dryas is not reflecting precisely the sea-surface water temperature. Another factor must play the dominant role here, probably nutrients.
... However, regardless of how the original founding population was established, the evidence presented here suggests strong endemism and genetic plasticity among the populations dwelling in the Arctic Ocean environment. Sympatric speciation, following the initial arrival of the founding population(s), may account for some of the remarkable radiation in skeletal morphology reported here; including the possibility that the local environmental regime and competitive interactions among the polycystines may have favored character displacement during early stages of speciation (Brown and Wilson, 1956) as documented for a high latitude nassellarian genus (Kellogg, 1975). As noted above, it is likely that these morphological changes have taken place in a relatively narrow window of geological time (from c. 10,000 -9000 14 C YBP to present, the Holocene). ...
Evidence, based on the species and high rank taxa composition and level of domination, skeletal morphological diversity and distributional data of radiolaria from sediment samples, is presented in support of a hypothesis of endemism for the Arctic polycystine fauna, especially arctic actinommids, as presented in the Discussion section. The arctic assemblages have low diversity, few species and very high level of domination of Actinommidae and Cannobotryidae. Two new endemic species, Actinomma georgii and A. turidae, are described based on their unique skeletal morphology. Although the geographic origins of these novel actinommids cannot be determined precisely based on existing knowledge of radiolarian reproductive processes and population biology, the preponderance of evidence presented here suggests that the unique features of the Arctic Ocean environment may contribute to elevated local speciation, and that the remarkable variability in skeletal morphology of Arctic Ocean actinommids may be enhanced by strong environmental selection pressures favoring relatively rapid speciation of polycystines in this high latitude oceanic regime. These actinommid species, including Actinomma boreale, without a 4th shell, are considered to be endemic and reproducing within the Arctic Ocean, suggesting that the two new species are environmentally adapted only to the particular environment of the Arctic Ocean. By contrast, A. boreale without a 4th shell is likely less adapted to this oceanic regime.
... Eucyrtidium calvertense (PI. 1, fig. 3) has been described by numerous authors (Martin, 1904;Hays, 1965;Kellogg, 1976), but always from middle and high latitude sediments. In the Oman margin sediments, it is consistently present throughout the S. peregrina and S. pentas Zones and rare, possibly reworked, specimens can be found in the Pleistocene. ...
The radiolarian assemblages are peculiar in that numerous common tropical forms, some of which are biomarkers, are absent or very rare. In addition, some species not usually found in tropical assemblages are present. These forms, indicative of upwelling conditions, fall into three categories: 1) endemic upwelling, 2) displaced temperate, and 3) enhanced tropical. Comparison of the Oman margin/Owen Ridge fauna with that recovered from the Peru margin upwelling area (ODP Leg 112) suggests that the assemblage may be globally diagnostic of upwelling conditions. The onset of upwelling is marked by the appearance of siliceous biota at about 11.9 Ma, and there is some indication of a decrease in the strength of the upwelling signal at about 9.6 Ma. A strong pulse in, or strengthening of, the upwelling mechanism is indicated by a marked fauna change at 4.7 Ma. There is a weaker signal, implying a change in upwelling conditions, at about 1.5 Ma. -from Author
... On islands where these species co-occur, however, G. fortis has a substantially larger bill than G. fuliginosa (Lack 1947;Grant 1986). This divergence of phenotypes, a pattern termed character displacement by Brown and Wilson (1956), is commonly observed in plants and animals (e.g., Schoener 1970;Eldredge 1974;Fenchel 1975;Kellogg 1975;Schindel and Gould 1977;Roughgarden et al. 1983;Schluter and McPhail 1992;Armbruster et al. 1994;Robinson and Wilson 1994;Adams and Rohlf 2000;Losos 2000). ...
Abstract Biologists have long known that closely related species are often phenotypically different where they occur together, but are indistinguishable where they occur alone. The causes of such character displacement are controversial, however. We used polyphenic spadefoot toad tadpoles (Spea bombifrons and S. multiplicata) to test the hypothesis that character displacement evolves to minimize competition for food. We also sought to evaluate the role of phenotypic plasticity in the mediation of competitive interactions between these species. Depending on their diet, individuals of both species develop into either a small-headed omnivore morph, which feeds mostly on detritus, or a large-headed carnivore morph, which specializes on shrimp. Laboratory experiments and surveys of natural ponds revealed that the two species were more dissimilar in their tendency to produce carnivores when they occurred together than when they occurred alone. This divergence in carnivore production was expressed as both character displacement (where S. multiplicata's propensity to produce carnivores was lower in sympatry than in allopatry) and as phenotypic plasticity (where S. multiplicata facultatively enhanced carnivore production in S. bombifrons, and S. bombifrons facultatively suppressed carnivore production in S. multiplicata). In separate experiments, we established that S. bombifrons (the species for which carnivore production was enhanced) was the superior competitor for shrimp. Conversely, S. multiplicata (the species for which carnivore production was suppressed and omnivore production enhanced) was the superior competitor for detritus. These results therefore demonstrate that selection to minimize competition for food can cause character displacement. They also suggest that both character displacement and phenotypic plasticity may mediate competitive interactions between species.
One method of increasing the resolving power of paleontological inquiries is to assess the time distribution, or phenology, of perispeciational change. The rationale for this test is that, while concentration of morphologic change around the time of speciation is consistent with both known microevolutionary mechanisms and punctuated equilibria, punctuated equilibrium theory presupposes that most of the change occurs either before or during initial allopatry to produce morphologically static taxa. Considerable change in the initial phases of speciation could also result from known microevolutionary mechanisms, but if significant change occurs in the neosympatric phase, or at any time after the species have become differentiated, then that change is best explained by known microevolutionary mechanisms.
Amount and rate of morphologic change during each phase of the allopatric speciation process were determined for two cognate species of the radiolarian genus Eucyrtidium. In this case, morphologic change accruing to these species during the neosympatric phase was 2-3 times as great as that which occurred during the initial allopatric phase. Morphologic trends in both these species during the allopatric phase differed significantly from a random walk. The size differential that characterized this speciation event was not the product of a single large step early in the process but of a disproportionate number of small steps in one direction during neosympatry. Therefore, the hypothesis of no statistically significant change following the “first stage” of speciation, which is a major tenet of punctuated equilibrium theory, is falsified for this case.
The most important topics discussed thus far by community paleoecologists are: community approach to paleoenvironmental reconstruction, community development in evolutionary time, and community constraints upon species evolution. The first step in community-paleoecological analysis is to reconstruct the paleocommunity or paleoecosystem. However there are severe methodological limitations to any inference drawn from the composition and structure of a fossil assemblage. These result from various taphonomic biases. These constraints upon reliability of a community-paleoecological analysis are the least severe in the case of Cenozoic (and possibly Cretaceous) tropical to subtropical, molluskdominated, subtidal, benthic communities.
The basic assumption of community paleoecology is that communities or biocoenoses represent a distinct, real level of biotic organization achieved through ecological integration of and coevolution among the species. This assumption seems to be invalid for two reasons. (1) The actual degree of community integration is in general insufficient to induce any driving forces for a structural development as predicted by the system theory. (2) The concept of biological reality and distinctness of the community level of biotic organization implies assignment of a significant role to group selection. The assumption that ecological communities achieve with time an equilibrium state representing an optimum habitat partitioning among the component species is invalid, at least as a generalization. This idea is largely falsified and refuted by a variety of ecological studies. Ecological communities are then merely an epiphenomenon of the overlap in distributional patterns of various organisms. There is no intrinsic, biotic mechanism inducing community dynamics in either ecological, or evolutionary time.
In spite of this conclusion, the so-called “community approach” under favorable taphonomic conditions is among the most reliable methods of paleoenvironmental reconstruction, and the data on so-called “community evolution” are relevant to the problem of a relationship between actually realized niche patterns and their environmental framework. The latter problem can also be approached through analysis of longevity-frequency-distributions of chronospecies found living together in various habitats. A preliminary investigation may indicate that the precondition to optimization of niche dimensions through coevolution among ecologically related species was met in subtidal benthic habitats but not in pelagic ones. To account for a niche subdivision among planktonic organisms, one has therefore to invoke a stochastic pattern of speciation rather than coevolutionary mechanisms.
Unlike most organisms, marine phytoplankton experience nearly deterministic rates of biotic interactions mediated by stochastic rates of turbulence. Yet studies of phytoplankton evolution have largely ignored biotic interactions, whereas studies of phytoplankton ecology have largely ignored evolutionary constraints. This review will attempt to integrate the opposing and complementary selective forces experienced by phytoplankton due to biotic and abiotic parameters over ultimate (evolutionary) and proximate (ecological) time scales. Attention will be focused on biotic interactions experienced by siliceous phytoplankton and the influence of these interactions on coexistence and local extinction (the ecological time framework), and diversification and species selection (the evolutionary time framework). The principal topics of discussion include the significance of biotic interactions among phytoplankton to the mechanisms of species displacement, species coexistence, the maintenance of species diversity, the selection of life history characteristics, and the mode and rate of evolution. A case study developed from a Paleogene phytoplankton assemblage is presented to illustrate that understanding the mechanisms of species interactions is requisite to a comprehensive interpretation of temporal changes in morphology, species dominance, and diversity. [For reviews of the physiology, ultrastructure, and distribution of siliceous marine phytoplankton, the reader is referred to Werner (1977), Bold and Wynne (1978), Morris (1980), Falkowski (1980), and Tappan (1980)].
Biological classification has always been concerned with expressing relationships between organisms, living and fossil, in a system that provided a foundation for further study and generalization. The foundations and mode of expression of the resulting classification have not always been the same. The Linnean hierarchy provided a formal scheme of ranking groups within groups, but the exact rules of the hierarchy depended on the accepted theory underlying biological classification. With the acceptance of organic evolution after 1859, the theory underlying classification modified from that of ideal typology to organic evolution. Yet the exact nature of classificatory schemes varied with the state of knowledge of evolutionary mechanisms and with the acceptance of diverse combinations of these mechanisms as crucial for biological classification. Thus all of the major modern approaches to biological classification are regarded as evolutionary, and the designation of one as classical evolutionary classification, or more simply as evolutionary classification, does not imply that the other approaches of phenetics or cladistics (phylogenetic classification) are not based upon organic evolution.
In the past decade, evolutionary paleoecology has shifted away from corroborative research of the 'me-too-ecology' type towards its proper domain - the evolutionary consequences of ecological properties, roles, and strategies at the individual, population, community, and species levels. The science of evolutionary paleoecology tests for linkage between a species' ecology and its macroevolutionary history. Do the ecological characters of species within clades influence differntial rate dynamics, particularly rates of faunal turnover and diversification? Intellectual coequality, once hampered by the misunderstanding that the role of paleoecology is to find examples of past ecology imperfectly entombed in the fossil record, is strengthened by the increasing number of evolutionary ecologists who have called for explicit paleontological contributions to resolve theoretical issues. The fossil record provides a necessary perspective to an understanding of process.-Author
Morphological consequences of hybridization were studied in a group of three interbreeding species of Darwin's finches on the small Galápagos island of Daphne Major in the inclusive years 1976 to 1992. Geospiza fortis bred with G. scandens and G. fuliginosa. Although interbreeding was always rare (< 5%), sufficient samples of measurements of hybrids and backcrosses were accumulated for analysis. Five beak and body dimensions and mass were measured, and from these two synthetic (principal-component) traits were constructed. All traits were heritable in two of the interbreeding species (G. fuliginosa were too rare to be analyzed) and in the combined samples of F, hybrids and backcrosses to G. fortis. In agreement with expectations from a model of polygenic inheritance, hybrid and backcross classes were generally phenotypically intermediate between the breeding groups that had produced them. Hybridization increased additive genetic and environmental variances, increased heritabilities to a moderate extent, and generally strengthened phenotypic and genetic correlations. New additive genetic variance introduced by hybridization is estimated to be two to three orders of magnitude greater than that introduced by mutation. Enhanced variation facilitates directional evolutionary change, subject to constraints arising from genetic correlations between characters. The Darwin's finch data suggest that these constraints become stronger when species with similar proportions hybridize, but some become weaker when the interbreeding species have different allometries. This latter effect of hybridization, together with an enhancement of genetic variation, facilitates evolutionary change in a new direction.
Marine planktonic microfossils have provided some of the best examples of evolutionary rates and patterns on multi-million-year time scales, including many instances of gradual evolution. Lineage splitting as a result of speciation has also been claimed, but all such studies have used subjective visual species discrimination, and interpretation has often been complicated by relatively small sample sizes and oceanographic complexity at the study sites. Here we analyze measurements on a collection of 10,200 individual tests of the Eocene planktonic foraminifer Turborotalia in 51 stratigraphically ordered samples from a site within the oceanographically stable tropical North Pacific gyre. We use novel multivariate statistical clustering methods to test the hypothesis that a single evolutionary species was present from 45 Ma to its extinction ca. 34 Ma. After identification of a set of biologically relevant traits, the protocol we apply does not require a prior assignment of individuals to species. We find that for most of the record, contemporaneous specimens form one morphological cluster, which we interpret as an evolving species that shows quasi-continuous but non-directional gradual evolutionary change (anagenesis). However, in the upper Eocene from ca. 36 to ca. 34 Ma there are two clusters that persistently occupy distinct areas of morphospace, from which we infer that speciation (cladogenesis) must have occurred.
In this paper, we present detailed quantitative studies of evolutionary changes over all or part of the stratigraphic ranges of five fossil radiolarian species from Pacific deep-sea sediment cores. Each of these species shows some variation of a distinctive evolutionary pattern: increase in size of measured morphologic characters, preceded and/or followed by an interval during which little or no significant change occurred.
One of the species studied (
Eucyrtidium matuyamai
) was allopatrically differentiated from another (
Eucyrtidium calvertense
). The others (
Calocycletta caepa, Pterocanium prismatium
and
Pseudocubus vema
) underwent phyletic change within a single lineage. Those species undergoing phyletic change towards larger size maintained almost constant variability of shell size over long periods of time, including periods of both rapid and extremely slow evolution. This constancy of variability suggests that diminution of selection against larger size may have acted as a stimulus to size increase. In contrast,
E. calvertense
decreased in variability during evolution towards smaller shell size. We believe this decrease may be interpreted as the result of two factors: (1) strong selection against larger size apparently exerted on this species by its direct descendant,
E. matuyamai
, during the neosympatric phase of speciation and (2) continuation of previous selection against very much smaller size.
Morphometric examination of cladogenesis and plyletic evolution in two late Neogene sister lineages of marine microfossils (Pterocanium prismatium and P. charybdeum, Radiolaria) from two equatorial Pacific sediment cores was undertaken to better understand the rate of cladogenesis and its relation to subsequent phyletic change. The origin of P. prismatium from P. charybdeum approx 4 Ma ago has been estimated to take place over an interval of approx 500 000 yr. Results show that the speciation event consists of two distinct phases. The first phase, cladogenesis, occurred relatively rapidly (on the order of 50 000 yr). A second phase of relatively rapid divergent phyletic evolution away from the commmon ancestral state followed in both descendant branches and continued for at least 50 000 yr after completion of the cladogenetic event. Net evolutionary rates over the next 2 ma appear to be much lower. Individual characters change by as much as two population standard deviations during cladogenesis, and by a total of approximately three standard deviations over 2.5 ma of phyletic evolution. Up to five population standard deviations of change during = or <50 000 yr of cladogenesis, and seven additional standard deviations of phyletic change over 500 000 yr are observed in multivariate (discriminant function) indices of morphologic difference. The measured pattern does not appear to be either strictly 'punctuated' or strictly 'gradual', but instead show features of both hypotheses.-Author
Argues that the history of life does not necessarily record an improvement in competitive abilities through time; that the idea of large-scale competitive replacements by the appearance of key adaptations is not supported by the evidence; and that the other macroevolutionary models that involve competition as a major factor are open to question. The author criticises the assumption that competition has a central role in macroevolution, and questions the use of microevolutionary concepts in describing major events in evolution.-from Author
Abstract Character displacement, in which coevolution of similar species alters their phenotypes, can be difficult to identify on the basis of observational data alone. In two-species systems, the most commonly identified (i.e., classic) resulting pattern is greater phenotypic difference between species in sympatry than allopatry. We show that restricting studies to this pattern may exclude many instances of character displacement, particularly in the presence of spatial environmental gradients. We present four spatial models of character displacement in quantitative traits affecting competition and hybridization between the species. Our models highlight the connections between range limits and character displacement in continuous space. We conclude that the classic pattern is less likely to occur for a trait affecting resource acquisition than for a trait affecting mate choice. We also show that interspecific hybridization (when hybrids are inviable), even in very small amounts, has marked effects on the shape and stability of borders between species and the nature of character displacement. A survey of the empirical literature shows that character displacement studies often lack analysis of spatial phenotype and abundance data. We recommend more careful spatial sampling in character displacement studies, and we illustrate how comparison of clines in mean phenotype in sympatry and allopatry can be used to suggest the action of character displacement.
Body size is a central feature of any organism, reflecting its physiology, ecology and evolutionary history. Marine microplankton are major contributors to the particulate inorganic carbonate (foraminifers and coccolithophorids) and opal flux (radiolaria and diatoms) in the ocean and, hence, size changes in these organisms can influence global biogeochemical cycles. This paper is discussing abiotic influences on micro- and macroecological size changes among major marine plankton groups, linking these to evolutionary size changes during the Neogene. We review the patterns and outline the causes of size changes geographically and through time in coccolithophorids, foraminifers and radiolarians. The main feature of the Neogene size record is a dramatic size increase in foraminifers, a similarly dramatic reduction in the size range of coccolithophorids and highly variable size patterns in radiolarians. We argue that the observed pattern is too complex to be explained by a simple common forcing and propose that speculations on the response of oceanic biomineralisation to global warming have to consider the scales at which marine plankton evolve.
The Pleistocene extinction of the widespread organ-pipe Montastraea coral had measurable morphological and ecological effects on surviving lineages of the Montastraea ''annularis" species complex. Extinction of the organ-pipe Montastraea occurred after more than 500,000 years of dominance in the shallow-water reef habitat of Barbados. Extinction resulted in a morphological shift of the columnar Montastraea lineage from thick to thin columns in modern reef environments, Pleistocene colonies of the columnar morphotype sympatric with organ-pipe Montastraea showed greater column widths than those in allopatry. We subjected our data to a number of criteria for interpreting the morphological shift as character release following lifting of competitive pressure after extinction. The morphological differences do not appear to be due either to chance or to physical properties of the marine environment. Differential local extinction and recolonization of four members of the species complex did not occur on Barbados, so that the species coexisted and appear to have coevolved between more than 600,000 and 82,000 years ago. The morphological shift is related to coral growth form and growth rate, and thus reflects the acquisition of a primary resource in corals-lights. Character release occurred at the same oceanic Caribbean island (Barbados) where environments have fluctuated with similar variance throughout the period of coexistence. Not only has competition among living members of the Montastraea "annularis" species complex been convincingly demonstrated, but trends in relative abundance among fossil members of the species complex strongly suggest that a competitive hierarchy was operating during their Pleistocene coexistence on Barbados. We also observed an ecological analogue to character release on another Caribbean island, Curacao, The distribution and abundance of living columnar M. annularis s.s. and massive M. faveolata from the leeward reef crest in Curacao is greater now than in the Pleistocene, when organ-pipe Montastraea dominated this shallow-water reef habitat. Extinction of the faster growing, shallow-water organ-pipe Montastraea resulted in higher abundance of the columnar Montastraea lineage in shallow-water habitats, where it shifted its morphology to one adapted to high light levels. The species extinction released surviving lineages from a competitive network that had resulted in lower rank abundance in the Pleistocene community and enhanced abundance of both columnar M. annularis s.s. and AT faveolata in modern communities. Full validation of our interpretation of character release must await experiments that demonstrate whether phenotypic differences between populations have a genetic basis. However, we believe the results of this study point to the important, yet heretofore neglected, role that biological interactions have played in the evolution of closely related reef coral species.
Character displacement, in which coevolution of similar species alters their phenotypes, can be difficult to identify on the basis of observational data alone. In two-species systems, the most commonly identified (i.e., classic) resulting pattern is greater phenotypic difference between species in sympatry than allopatry. We show that restricting studies to this pattern may exclude many instances of character displacement, particularly in the presence of spatial environmental gradients. We present four spatial models of character displacement in quantitative traits affecting competition and hybridization between the species. Our models highlight the connections between range limits and character displacement in continuous space. We conclude that the classic pattern is less likely to occur for a trait affecting resource acquisition than for a trait affecting mate choice. We also show that interspecific hybridization (when hybrids are inviable), even in very small amounts, has marked effects on the shape and stability of borders between species and the nature of character displacement. A survey of the empirical literature shows that character displacement studies often lack analysis of spatial phenotype and abundance data. We recommend more careful spatial sampling in character displacement studies, and we illustrate how comparison of clines in mean phenotype in sympatry and allopatry can be used to suggest the action of character displacement.
Some morphological differences between closely related species living in the same environment have been enhanced by natural selection resulting from competition between the species or the negative effects of interbreeding. These evolutionary changes are known as ecological and reproductive character displacement, respectively. Ecological character displacement, the subject of this article, helps us to understand how complex communities are built up from simpler ones through ecological adjustments of the constituent species. It also may be involved in the late stages in speciation when formerly allopatric populations come together in sympatry. Examples are given from studies of birds in nature and sticklebacks in experiments. There are few cases of ecological character displacement in nature where the evidence is sufficiently strong to demonstrate evolution by natural selection and to rule out alternative explanations of the causes. These have been supplemented by experiments: there is scope and need for more.
Key Concepts
Character displacement is a process of evolutionary divergence of coexisting species.
Competition for resources, such as food, is reduced as a result of divergence.
Natural selection causes the evolutionary change.
Closely related species differ in morphology more in sympatry than in allopatry.
Experiments attempt to recreate conditions that are conducive to character displacement in nature.
Solitary species are released from competition and broaden their ecological niches.
Character displacement helps to explain how complex communities of potential competitors develop from simple ones.
Character displacement is one of several types of evolutionary adjustments made by coexisting species.
Its signature should be seen most clearly in young adaptive radiations.
The main question about character displacement is not whether it occurs but how important it is.
The abrupt, widespread, and simultaneous extinction of radiolarian species makes them ideal stratigraphic markers. Five species became extinct in the North Pacific during the last 3 m.y. Four of these are used to define four stratigraphic zones. The boundary between the oldest two zones correlates with the Pliocene/Pleistocene boundary, as defined in southern Italy. These zones can be related through paleomagnetic stratigraphy to previously established radiolarian and foraminiferal zonations.
One species (Eucyrtidium matuyamai) evolved and became extinct during the last 2.5 m.y. Its evolution can be related to the invasion of and adaptation to a new habitat. The extinction of E. matuyamai shows a striking correlation with the magnetic reversal at the base of the Jaramillo event. The rapid evolution of this species probably reduced the genetic variability of the population, making it more vulnerable to extinction than other less rapidly evolving species. The environmental change that caused the extinction is unclear; however, there is suggestive evidence that it is in some way related to a reversal of the earth’s field. If reversals cause abrupt environmental changes, they may have played an important selective role through geologic time.
In this paper, we present detailed quantitative studies of evolutionary changes over all or part of the stratigraphic ranges of five fossil radiolarian species from Pacific deep-sea sediment cores. Each of these species shows some variation of a distinctive evolutionary pattern: increase in size of measured morphologic characters, preceded and/or followed by an interval during which little or no significant change occurred.
One of the species studied (
Eucyrtidium matuyamai
) was allopatrically differentiated from another (
Eucyrtidium calvertense
). The others (
Calocycletta caepa, Pterocanium prismatium
and
Pseudocubus vema
) underwent phyletic change within a single lineage. Those species undergoing phyletic change towards larger size maintained almost constant variability of shell size over long periods of time, including periods of both rapid and extremely slow evolution. This constancy of variability suggests that diminution of selection against larger size may have acted as a stimulus to size increase. In contrast,
E. calvertense
decreased in variability during evolution towards smaller shell size. We believe this decrease may be interpreted as the result of two factors: (1) strong selection against larger size apparently exerted on this species by its direct descendant,
E. matuyamai
, during the neosympatric phase of speciation and (2) continuation of previous selection against very much smaller size.
Magnetic stratigraphy of 15 oriented cores from the equatorial Pacific was determined as far back as the Gilbert reversed-polarity epoch. Ranges of selected species of four major microfossil groups (diatoms, silicoflagellates, foraminifers and Radiolaria) are compared with the record of geomagnetic reversals during the last 4.5 m. y. in eastern equatorial Pacific deep-sea cores. Characteristics of the fossil assemblages are used as criteria for recognition of most of the paleomagnetic reversals that occurred during this interval. Two zones of major paleontological change occur characterized by extinctions of several species and coiling direction changes in some foraminifers. The first change comes in the middle of the Gauss normal magnetic series (about 3 m.y. B.P.) and the second near the Olduvai magnetic event (about 2.0 m.y. B.P.). Seven equatorial foraminiferal species, two radiolarian species, and two diatom species become extinct near reversals. The establishment of the true chronostratigraphic relationships of these selected microfossil species allows us to date zonations of previous authors and provides absolute dates that can be used in worldwide correlation of marine sediments. The percentage of calcium carbonate was determined throughout the lengths of four cores. Eight distinct carbonate cycles are present in the Brunhes series, having periodicities of about 75,000 years in the upper Brunhes to over 100,000 years in the lower Brunhes. It is possible to correlate these carbonate cycles among our cores and also to correlate them with the previous work of Arrhenius who equated the carbonate peaks with glacial stages and the troughs with interglacial stages. This interpretation is supported by paleomagnetic and C14 dating of the last carbonate high which is synchronous with the Wisconsin glaciation (80,000 to 11,500 years B.P.). It, therefore, is probable that there were eight major glacial fluctuations during the last 700,000 years. During the last 400,000 years there is good correlation between the carbonate cycles of the Pacific and evidence of climatic fluctuations in the Atlantic established by Ericson and Wollin (1968) and Emiliani (1966) based on fossil abundances and oxygen isotope ratios, respectively. The rates of sedimentation during the Brunhes series range between 3.5 mm/1000 years for siliceous ooze to 17.5 mm/1000 years for highly calcareous sediment.
The Antarctic Polar Front (Antarctic Convergence) exerts a powerful influence on the distribution of Radiolaria in the southern seas. This influence is seen in the sediments somewhat north of the mean position of the Front, by a mixed zone which forms a transition from Antarctic species confined to the cold waters south of the Front to warm-water species north of the Front, most of which are cosmopolitan. The approximate parallelism of the mixed zone with the mean position of the Front is seriously modified only by the Falkland Current. The mixed zone may be caused by mixing of Antarctic and sub-Antarctic surface waters or by the northward transport of the tests of dead Antarctic species in the intermediate or bottom waters.
V28-239 core from cruise 28 of R / V Vema preserves a detailed oxygen-isotope and paleomagnetic record for all of the Pleistocene Epoch. The entire 21-m-long core has been analyzed at 5-cm intervals. Glacial stage 22, above the Jaramillo magnetic event, may represent the first major Northern Hemisphere continental glaciation of middle Pleistocene character. Prior to this, higher frequency glacial events extend to near the level of the Olduvai magnetic event. Glacial events of less regular frequency extend to the bottom of the core, which represents late Pliocene time. Fluctuations in carbonate dissolution intensity occur throughout the core with a similar frequency to the oxygen-isotope fluctuations.
Part I. Description: 1. Galapagos scene 2. Classification 3. Ecology 4. Female plumage 5. Male plumage and sexual selection 6. Beak differences and food 7. Size differences between island forms 8. Size differences between species 9. Individual variation 10. Hybridisation 11. An evolutionary tree Part II. Interpretation: 12. The origin of the Galapagos fauna 13. The origin of subspecies 14. The origin of species 15. The persistence of species 16. Adaptive radiation Summary Acknowledgements Tables of measurements References Indexes.
The synthetic assumption that macroevolutionary changes can be explained completely by known microevolutionary mechanisms is widely accepted, but it still lacks supporting evidence at the species level. The radiation of the subfamily Psittirostrinae of the Hawaiian honeycreepers is described as a supporting example in which major changes in their bill structure and feeding habits have occurred by a series of steps involving modifications on the species level and can be illustrated by existing taxa. The core concept for development of general macroevolutionary theory and for understanding particular cases of major evolutionary change is the arrangement of events and associated modifications into a probable sequence followed by the analysis of this sequence using known evolutionary mechanisms. The exact sequence or the choice of one of several possible sequences is not important. Rather it is the concept that major evolutionary changes, being the consequence of a series of events each of which dependent upon previous ones, can be analyzed properly only within the frame-work of a plausible sequence of events, changes and controlling evolutionary mechanisms.
Consideration of the possibilities and difficulties of detecting character displacement leads to a re-definition of the phenomenon; character displacement is the process by which a morphological character state of a species changes under Natural Selection arising from the presence, in the same environment, of one or more species similar to it ecologically and/or reproductively. This incorporates the principal ideas in the original definition given by Brown & Wilson (1956), but eliminates the restriction of making comparisons of the character states of a species in sympatry and allopatry.
The evidence for the ecological (competitive) aspect of character displacement is assessed by analyzing in detail the best documented and well publicized examples in the literature. Some of the examples either do not exhibit displaced characters or, if they do, the “displacement” can be interpreted in other and perhaps simpler ways; this applies to the so-called classical case of character displacement, Sitta tephronota and S. neumayer in Iran. Other examples, involving lizards and birds, constitute better evidence for character displacement, but in no single study is it entirely satisfactory. It is concluded that the evidence for the ecological aspect of character displacement is weak.
Convergence between two Pennsylvanian gastropod species; a multivariate mathematical approach
- Eldredge N.
ELDREDGE, N. 1968. Convergence between two
Pennsylvanian gastropod species; a multivariate mathematical approach. J. Paleont. 42:
559-565.
Competition between sympatric species ofEucyrtidiumin deep-sea microfossil sequences
- D E Kellogg
- Robbins
KELLOGG, D. E., AND J. ROBBLNs. 1975. Competition between sympatric species of Eucyrtidium
in deep-sea microfossil sequences. (in prep.)
Competition between sympatric species of Eucyrtidium in deep-sea microfossil sequences. (in prep.) LACK, D. 1947. Darwin's finches
- And J Robblns
KELLOGG, D. E., AND J. ROBBLNs. 1975. Competition between sympatric species of Eucyrtidium
in deep-sea microfossil sequences. (in prep.)
LACK, D. 1947. Darwin's finches. Cambridge
University Press, Cambridge, England.
Paleomagnetism of cores from the North Pacific
- N D Opdyke
- . H Foster
OPDYKE, N. D., AND J. H. FOSTER. 1970. Paleomagnetism of cores from the North Pacific.
p. 83-119 In J. D. Hays (ed.), Geologic investigations of the North Pacific, Geol. Soc.
Am. Memoir 126.
Investigations of late quaternary paleooceanography and paleoclimatology
- Hays
Hays (eds.), Investigations of late quaternary
paleooceanography and paleoclimatology. Geol.
Soc. Am. Memoir 145.
Microevolutionary mechanisms in the evolution of Miocene to Recent Radiolaria from Pacific deep-sea cores. Doctoral dissertation
- D E Kellogg
KELLOGG, D. E. 1973. Microevolutionary mechanisms in the evolution of Miocene to Recent
Radiolaria from Pacific deep-sea cores. Doctoral dissertation, Columbia University, 376 p.
- G C Martin
MARTIN, G. C. 1904. Radiolaria. Maryland
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- N D J H Opdyke
- Foster